With the holidays approaching, you may have that feeling of anticipation as you wonder what gifts you might receive.

In California, the surprises don’t end there.

December can be full of precipitation expectations—sometimes they’re met, sometimes they fall short, and sometimes they’re exceeded.  

December Climatology:

Looking at the historical record of California’s December precipitation from 1895 to 2013 [1], you can see just how mixed the month can be. Some Decembers barely manage half an inch of rain, while others leave the state drenched.

Take 1955, for example: more than 10 inches of precipitation fell in December alone, setting a high mark that few other years have come close to. The average December precipitation for that period (red shading)—about 3.63 inches—gives some perspective, but the plot above shows just how wildly individual years can swing.

Yet, looking at the long-term trend, December precipitation has been remarkably steady over the past century. The slope of the trend line is tiny (just 0.0024 inches per year) showing that, despite the big swings from year to year, the average amount of rain in December hasn’t changed much.

This Year So Far:

The image below is from the California Water Watch data query tool [2]. The average precipitation is shaded blue, last year’s accumulation curve in red, and this year in green. You can see that December began quietly last year, but precipitation picked up mid-month in 2024 and ended above average. This year, with significant precipitation inNovember, the water year was off to a quick start. However, the first half of December has been relatively flat.  

A Little Context:

Of course, in California, a single month never defines a final water year outcome. With the wet season stretching from December through March, historical data proves that what happens in December isn’t necessarily a strong predictor of the months that follow.

We’ll just have to sit back and see what surprises December has in store—but even when December is unpredictable, our water year forecast has been on target for nine straight years. If you’d like to learn more, set up a meeting today!

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[1] Historical December precipitation data: California Department of Water Resources, Precipitation Records 1895–2013.

[2] Current-year precipitation data: California Water Watch Data Query Tool, accessed December 2025.

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